I am building some objects in JavaScript and pushing those objects into an array, I am storing the key I want to use in a variable then creating my objects like so:
var key = "happyCount";
myArray.push( { key : someValueArray } );
but when I try to examine my array of objects for every object the key is "key" instead of the value of the variable key. Is there any way to set the value of the key from a variable?
Fiddle for better explanation:
http://jsfiddle.net/Fr6eY/3/
You need to make the object first, then use [] to set it.
var key = "happyCount";
var obj = {};
obj[key] = someValueArray;
myArray.push(obj);
UPDATE 2021:
Computed property names feature was introduced in ECMAScript 2015 (ES6) that allows you to dynamically compute the names of the object properties in JavaScript object literal notation.
const yourKeyVariable = "happyCount";
const someValueArray= [...];
const obj = {
[yourKeyVariable]: someValueArray,
}
In ES6, you can do like this.
var key = "name";
var person = {[key]:"John"}; // same as var person = {"name" : "John"}
console.log(person); // should print Object { name="John"}
var key = "name";
var person = {[key]:"John"};
console.log(person); // should print Object { name="John"}
Its called Computed Property Names, its implemented using bracket notation( square brackets) []
Example: { [variableName] : someValue }
Starting with ECMAScript 2015, the object initializer syntax also
supports computed property names. That allows you to put an expression
in brackets [], that will be computed and used as the property name.
For ES5, try something like this
var yourObject = {};
yourObject[yourKey] = "yourValue";
console.log(yourObject );
example:
var person = {};
var key = "name";
person[key] /* this is same as person.name */ = "John";
console.log(person); // should print Object { name="John"}
var person = {};
var key = "name";
person[key] /* this is same as person.name */ = "John";
console.log(person); // should print Object { name="John"}
var key = "happyCount";
myArray.push( { [key] : someValueArray } );
Use this.
var key = 'a'
var val = 'b'
console.log({[key]:val})
//a:'b'
In ES6 We can write objects like this
const key= "Name";
const values = "RJK"
const obj = {
[key]: values,
}
In TypeScript, it should look something like this
let title ="Current User";
type User = {
[key:string | number | symbol]: any
};
let myVar: User = {};
myVar[ title ] = "App Developer";
console.log(myVar)// Prints: { Current User:"App Developer"}
let key = "name";
let name= "john";
const obj ={
id:01
}
obj[key] = name;
console.log(obj); // output will {id:01,name:"john}
Use square brackets shown it will set as key
The Reality
The problem in JS is simply that:
{ x: 2 }
is THE SAME as:
{ "x": 2 }
(even if you have x a variable defined!)
Solution
Add square brackets [] around the identifier of the key:
var key = "happyCount";
myArray.push( { [key] : someValueArray } );
(Nowadays the keyword var is not much used, so please use instead const or let)
tldr;
Related
I have code like this.
var key = "anything";
var object = {
key: "key attribute"
};
I want to know if there is a way to replace that key with "anything".
like
var object = {
"anything": "key attribute"
};
In ES6, use computed property names.
const key = "anything";
const object = {
[key]: "key attribute"
// ^^^^^ COMPUTED PROPERTY NAME
};
Note the square brackets around key. You can actually specify any expression in the square brackets, not just a variable.
Yes. You can use:
var key = "anything";
var json = { };
json[key] = "key attribute";
Or simply use your second method if you have the values at hand when writing the program.
On modern Javascript (ECMAScript 6) you can sorround the variable with square brackets:
var key = "anything";
var json = {
[key]: "key attribute"
};
This should do the trick:
var key = "anything";
var json = {};
json[key] = "key attribute";
Solution:
var key = "anything";
var json = {};
json[key] = "key attribute";
Recently needed a solution how to set cookies passing the dynamic json key values.
Using the https://github.com/js-cookie/js-cookie#json, it can be done easily.
Wanted to store each selected option value of user in cookie, so it's not lost in case of tab or browser shutting down.
var json = {
option_values : {}
};
$('option:selected').each(function(index, el) {
var option = $(this);
var optionText = option.text();
var key = 'option_' + index;
json.option_values[key] = optionText;
Cookies.set('option_values', json, { expires: 7 } );
});
Then you can retrieve each cookie key value on each page load using
Cookies.getJSON('option_values');
Closures work great for this.
function keyValue(key){
return function(value){
var object = {};
object[key] = value;
return object;
}
}
var key = keyValue(key);
key(value);
Well, there isn't a "direct" way to do this...
but this should do it:
json[key] = json.key;
json.key = undefined;
Its a bit tricky, but hey, it works!
In Typescript I would like the myObj variable to be:
{'key01': 'value01'}
So I go ahead with:
let keyName = 'key01';
let myObj = {keyName: 'value01'};
console.log(myObj);
But the resulting variable is
{ keyName: 'value01' }
Can I use the value of the keyName variable to use as the key name for the variable myObj?
If you don't want to waste space with an extra line of code for defining the main object and then defining the custom key, you can use bracket notation inline.
let keyName = 'key01';
let myObj = { [keyName]: 'value01' };
console.log(myObj);
You can use the bracket notation property accessor:
let keyName = 'key01';
let myObj = {};
myObj[keyName] = 'value01';
console.log(myObj);
For TypeScript, use:
let keyName = 'key01';
let myObj:any = {};
myObj[keyName] = 'value01';
If you want to change the value of your object using the variable keyName you can use the following.
let keyName = "newValue";
let myObject = {keyName: "oldValue"}
myObject.keyName = keyName
console.log(myObject)
I think I've seen how to create a JSON object without first preparing it. This is how i prepare it:
obj = {
0:{
type:{}
},
1:{},
2:{}
};
Now I think I can insert a value like: obj.0.type = "type0"; But I'd like to create it while using it: obj['0']['type'] = "Type0";.
Is it possible, or do I need to prepare it? I'd like to create it "on the fly"!
EDIT
I'd like to create JS object "On the fly".
var obj = {};
obj.test = "test"; //One "layer" works fine.
obj.test.test = "test" //Two "layers" do not work... why?
obj = {
0:{
type:{}
},
1:{},
2:{}
};
Now i think i can insert value like: obj.0.type = "type0";
I guess you mean "assign" a value, not "insert". Anyway, no, you can't, at least not this way, because obj.0 is invalid syntax.
But I'd like to create it while using it: obj['0']['type'] = "Type0";
That's fine. But you need to understand you are overwriting the existing value of obj[0][type], which is an empty object ({}), with the string Type0. To put it another way, there is no requirement to provide an initialized value for a property such as type in order to assign to it. So the following would have worked equally well:
obj = {
0:{},
1:{},
2:{}
};
Now let's consider your second case:
var obj = {};
obj.test = "test"; //One "layer" works fine.
obj.test.test = "test" //Two "layers" do not work... why?
Think closely about what is happening. You are creating an empty obj. You can assign to any property on that object, without initializing that property. That is why the assignment to obj.test works. Then in your second assignment, you are attempting to set the test property of obj.test, which you just set to the string "test". Actually, this will work--because strings are objects that you can set properties on. But that's probably not what you want to do. You probably mean to say the previous, string value of obj.test is to be replaced by an object with its own property "test". To do that, you could either say
obj.test = { test: "test" };
Or
obj.test = {};
obj.test.test = "test";
You are creating a plain object in JavaScript and you need to define any internal attribute before using it.
So if you want to set to "Type0" an attribute type, inside an attribute 0 of an object obj, you cannot simply:
obj['0']['type'] = "Type0";
You get a "reference error". You need to initialize the object before using it:
var obj = {
0: {
type: ""
}
};
obj['0']['type'] = "Type0";
console.log(obj['0']['type']);
You could create your own function that takes key as string and value and creates and returns nested object. I used . as separator for object keys.
function create(key, value) {
var obj = {};
var ar = key.split('.');
ar.reduce(function(a, b, i) {
return (i != (ar.length - 1)) ? a[b] = {} : a[b] = value
}, obj)
return obj;
}
console.log(create('0.type', 'type0'))
console.log(create('lorem.ipsum.123', 'someValue'))
Is it necessary to create nested objects before using it?
Yes it is, at least the parent object must exist.
Example:
var object = {};
// need to assign object[0]['prop'] = 42;
create the first property with default
object[0] = object[0] || {};
then assign value
object[0]['prop'] = 42;
var object = {};
object[0] = object[0] || {};
object[0]['prop'] = 42;
console.log(object);
Create object with property names as array
function setValue(object, keys, value) {
var last = keys.pop();
keys.reduce(function (o, k) {
return o[k] = o[k] || {};
}, object)[last] = value;
}
var object = {};
setValue(object, [0, 'prop'], 42);
console.log(object);
How can I use a variable value as an object key?
For example, when adding an object dynamically to a Collection. When I to do it like this:
addToDB(type, account) {
Accounts.insert({type: account});
};
it doesn't work as the key can't be a variable here.
JavaScript object literal don't support dynamic keys.
Instead you can achieve the goal using :
var obj = {};
var key = "some key";
obj[key] = "test";
In your case:
addToDB(type, account) {
var obj = {};
obj[type] = account;
Accounts.insert(obj);
};
More details here:
Creating object with dynamic keys
This question already has answers here:
Accessing an object property with a dynamically-computed name
(19 answers)
Closed 4 months ago.
I'm pulling items out of the DOM with jQuery and want to set a property on an object using the id of the DOM element.
Example
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// Here is the problem
obj.name = value
})
If itemsFromDom includes an element with an id of "myId", I want obj to have a property named "myId". The above gives me name.
How do I name a property of an object using a variable using JavaScript?
You can use this equivalent syntax:
obj[name] = value
Example:
let obj = {};
obj["the_key"] = "the_value";
or with ES6 features:
let key = "the_key";
let obj = {
[key]: "the_value",
};
in both examples, console.log(obj) will return: { the_key: 'the_value' }
With ECMAScript 2015 you can do it directly in object declaration using bracket notation:
var obj = {
[key]: value
}
Where key can be any sort of expression (e.g. a variable) returning a value:
var obj = {
['hello']: 'World',
[x + 2]: 42,
[someObject.getId()]: someVar
}
You can even make List of objects like this
var feeTypeList = [];
$('#feeTypeTable > tbody > tr').each(function (i, el) {
var feeType = {};
var $ID = $(this).find("input[id^=txtFeeType]").attr('id');
feeType["feeTypeID"] = $('#ddlTerm').val();
feeType["feeTypeName"] = $('#ddlProgram').val();
feeType["feeTypeDescription"] = $('#ddlBatch').val();
feeTypeList.push(feeType);
});
There are two different notations to access object properties
Dot notation: myObj.prop1
Bracket notation: myObj["prop1"]
Dot notation is fast and easy but you must use the actual property name explicitly. No substitution, variables, etc.
Bracket notation is open ended. It uses a string but you can produce the string using any legal js code. You may specify the string as literal (though in this case dot notation would read easier) or use a variable or calculate in some way.
So, these all set the myObj property named prop1 to the value Hello:
// quick easy-on-the-eye dot notation
myObj.prop1 = "Hello";
// brackets+literal
myObj["prop1"] = "Hello";
// using a variable
var x = "prop1";
myObj[x] = "Hello";
// calculate the accessor string in some weird way
var numList = [0,1,2];
myObj[ "prop" + numList[1] ] = "Hello";
Pitfalls:
myObj.[xxxx] = "Hello"; // wrong: mixed notations, syntax fail
myObj[prop1] = "Hello"; // wrong: this expects a variable called prop1
tl;dnr: If you want to compute or reference the key you must use bracket notation. If you are using the key explicitly, then use dot notation for simple clear code.
Note: there are some other good and correct answers but I personally found them a bit brief coming from a low familiarity with JS on-the-fly quirkiness. This might be useful to some people.
With lodash, you can create new object like this _.set:
obj = _.set({}, key, val);
Or you can set to existing object like this:
var existingObj = { a: 1 };
_.set(existingObj, 'a', 5); // existingObj will be: { a: 5 }
You should take care if you want to use dot (".") in your path, because lodash can set hierarchy, for example:
_.set({}, "a.b.c", "d"); // { "a": { "b": { "c": "d" } } }
First we need to define key as variable and then we need to assign as key as object., for example
var data = {key:'dynamic_key',value:'dynamic_value'}
var key = data.key;
var obj = { [key]: data.value}
console.log(obj)
Related to the subject, not specifically for jquery though. I used this in ec6 react projects, maybe helps someone:
this.setState({ [`${name}`]: value}, () => {
console.log("State updated: ", JSON.stringify(this.state[name]));
});
PS: Please mind the quote character.
With the advent of ES2015 Object.assign and computed property names the OP's code boils down to:
var obj = Object.assign.apply({}, $(itemsFromDom).map((i, el) => ({[el.id]: el.value})));
ajavascript have two type of annotation for fetching javascript Object properties:
Obj = {};
1) (.) annotation eg. Obj.id
this will only work if the object already have a property with name 'id'
2) ([]) annotation eg . Obj[id] here if the object does not have any property with name 'id',it will create a new property with name 'id'.
so for below example:
A new property will be created always when you write Obj[name].
And if the property already exist with the same name it will override it.
const obj = {}
jQuery(itemsFromDom).each(function() {
const element = jQuery(this)
const name = element.attr('id')
const value = element.attr('value')
// This will work
obj[name]= value;
})
If you want to add fields to an object dynamically, simplest way to do it is as follows:
let params = [
{ key: "k1", value: 1 },
{ key: "k2", value: 2 },
{ key: "k3", value: 3 },
];
let data = {};
for (let i = 0; i < params.length; i++) {
data[params[i].key] = params[i].value;
}
console.log(data); // -> { k1: 1, k2: 2, k3: 3 }
The 3 ways to access the object value
We can output the object value by passing in the appropriate key. Because I used emoji as the key in my example, it's a bit tricky. So let's look at a easier example.
let me = {
name: 'samantha',
};
// 1. Dot notation
me.name; // samantha
// 2. Bracket notation (string key)
me['name']; // samantha
// 3. Bracket notation (variable key)
let key = 'name';
me[key]; // samantha
know more
If you have object, you can make array of keys, than map through, and create new object from previous object keys, and values.
Object.keys(myObject)
.map(el =>{
const obj = {};
obj[el]=myObject[el].code;
console.log(obj);
});
objectname.newProperty = value;
const data = [{
name: 'BMW',
value: '25641'
}, {
name: 'Apple',
value: '45876'
},
{
name: 'Benz',
value: '65784'
},
{
name: 'Toyota',
value: '254'
}
]
const obj = {
carsList: [{
name: 'Ford',
value: '47563'
}, {
name: 'Toyota',
value: '254'
}],
pastriesList: [],
fruitsList: [{
name: 'Apple',
value: '45876'
}, {
name: 'Pineapple',
value: '84523'
}]
}
let keys = Object.keys(obj);
result = {};
for(key of keys){
let a = [...data,...obj[key]];
result[key] = a;
}